239. Sliding Window Maximum

Difficulty: Hard

Frequency: N/A

Given an array nums, there is a sliding window of size k which is moving from the very left of the array to the very right. You can only see the k numbers in the window. Each time the sliding window moves right by one position.

For example,
Given nums = [1,3,-1,-3,5,3,6,7], and k = 3.

Window position                Max
---------------               -----
[1  3  -1] -3  5  3  6  7       3
 1 [3  -1  -3] 5  3  6  7       3
 1  3 [-1  -3  5] 3  6  7       5
 1  3  -1 [-3  5  3] 6  7       5
 1  3  -1  -3 [5  3  6] 7       6
 1  3  -1  -3  5 [3  6  7]      7

Therefore, return the max sliding window as [3,3,5,5,6,7].

Note:
You may assume k is always valid, ie: 1 ≤ k ≤ input array’s size for non-empty array.

Follow up:
Could you solve it in linear time?

Hint:

  1. How about using a data structure such as deque (double-ended queue)?
  2. The queue size need not be the same as the window’s size.
  3. Remove redundant elements and the queue should store only elements that need to be considered.

Test Cases:


Solution 1:

Data structure:
Steps:
Complexity:
Runtime:
Space:
Code:
class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        deque<int> dq;
        vector<int> results;
        for (int i = 0; i < nums.size(); i++) {
            if (!dq.empty() && dq.front() == i - k) dq.pop_front();
            while (!dq.empty() && nums[dq.back()] < nums[i]) {
                dq.pop_back();
            }
            dq.push_back(i);
            if (i >= k - 1) {
                results.push_back(nums[dq.front()]);
            }
        }
        return results;
    }
};

Solution 2:

Data structure:
steps:
Complexity:
Runtime:
Space:
Code:


Submission errors:

 

Things to learn:

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s